The idea of merging electronics with textiles and other flexible articles is not new, but problems are encountered in that textiles are not as dimensionally stable as firm PCBs formed from stiff materials. To add a level of firmness, connections between electronic textile (e-textile) devices are made using snaps or other single-point connectors aligned to individual conductive traces. However, single-point connectors create cost- and manufacturing-limitations on the way electronic signals are transmitted to a receiving device, making assembly and production less efficient and more costly.
Moreover, because microprocessors and most sensors are more compatible with PCBs, it has made it harder to assimilate the use of multi-pin electrical connections into the textile field, including wearable electronics. Compounding the difficulty, long-established PCB soldering technologies do not work with textile circuits, given that the high soldering temperatures (400 C and up) will melt or damage the substrates.
To further understand the challenge of establishing and maintaining electrical connections in a flexible material, consider a familiar product: flat panel monitors with liquid crystal displays (LCD). Such displays use a “zebra connector” or “z-axis conductive tape” containing microscale elements that conduct only through the thickness of the material, not laterally. For example, in a LCD, soft elastomeric connectors bring signals from hundreds of copper traces, positioned on the control PCB, to thin-film conductive oxide traces positioned on the glass screen. There is no need for soldering, nor for an expensive rigid plug-in connector, nor for precise alignment. However, the zebra connector method depends on the PCB and glass being rigid enough that the elastomer can be compressed by clamping. So while connections based on anisotropic conductive materials (ACM) like z-axis tape are feasible for flat panel displays, the principles do not work with textiles and other flexible, non-rigid materials. In short, Z-axis conductive tape was not designed for the porous surfaces of e-textiles, and clamping against a rigid surface would still be needed for reliable electrical contact using the tape.
According to present embodiments, anisotropic conductive thread (ACT) is a type of (ACM) suitable to provide both mechanical and electrical connections needed to assimilate textiles with electronics. ACT does so a manner that is both effective and cost-efficient. Further developments in applications of ACT to solve these problems in the field of textiles are described in more detail below.